334 THALLOPHYTES 



From the nodes the branches arise in whorls and some "branches 

 resemble leaves, while others elongate much more and resemble 

 the main axis. 



Their reprodv£Uon may be illustrated by following that of 

 Chara. There are no asexual spores, but the plant is propagated 

 vegetatively by special tuber-like branches which separate from 

 the nodes and grow into new plants. 



Sexual reproduction involves complex structures which are not 

 typical of Algae and which are the most distinguishing features 

 of the Stoneworts. Both antheridia and oogonia (Fig. 287) are 

 complex structures. Due to their size and color the sex organs 

 are visible to the unaided eye. Both are developed at the nodes 

 and often close together. 



The antheridium is an orange or reddish globular body with 

 a wall composed of eight triangular plate-like cells. From the 

 inner side of each of the wall cells there projects toward the 

 center of the antheridium a much elongated cell which bears a 

 terminal cell. The terminal cell, known as head cell, divides into 

 a number of cells and each of these produces a pair of long fila- 

 ments. Each filament consists of about 200 cells, each of which 

 forms a single sperm. When an antheridium is fully formed, its 

 interior is a tangle of filaments and the sperm output amounts 

 to many thousands. The sperm is a much elongated ciliated 

 structure, resembling the sperms of some of the more complex 

 plants more than those of ordinary Algae. 



The oogonium with its jacket is larger and more elongated 

 than the antheridium. The oogonia are often yellow but are not 

 so brightly colored as the antheridia. An oogonium contains one 

 large egg and much stored food in the form of starch and oil. 

 The oogonium is closely invested by cells which grow up from the 

 cells below and, as they elongate, wind spirally around the 

 oogonium, forming a close jacket around it and a crown at 

 its top. 



In fertilization the cells of the jacket spread apart at the 

 crown, so that the sperms can enter. After fertilization the 

 jacket hardens, and thus forms a nut-like case for the oospore. 

 When the oospore germinates, it does not form a new plant 

 directly but first forms a filament of cells, and the adult plant 

 arises as a branch from this filament. This feature is prominent 

 in the Bryophytes. 



